1. Field of the Invention
The present invention relates to a mechanic drive apparatus, and particularly relates to an infinitely variable-speed mechanic drive apparatus which is capable of providing a positive non-slip drive.
2. Description of the Related Art
It is known that in a lathe, the speed of rotation of the spindle, and therefore, the cutting speed of the tool can be controlled by using different types of drive mechanisms. Among them are a belt drive, a gear drive and a friction-drive mechanism. In the gear drive mechanism, a number of gears can be employed to provide a variety of speeds. Though the cutting speed of the tool can be controlled by suitable selection of the transmission ratio of the meshed gears in the gearbox, due to the fixed radius of the gears employed in the gearbox, no infinitely variable control over the transmission ratio can be obtained.
The friction-drive mechanism which can provide an infinitely variable control over the transmission ratio, might be a solution in case that a stepless control of the cutting speed of the tool is needed. However, in order to develop a sufficient frictional force at the point of contact to enable the friction wheels to transmit power, two friction wheels should be pressed together firmly. Otherwise, an undesirable large amount of slip will occur between the friction wheels. Another disadvantage in employing the friction-drive mechanism to control the speed of the tool is that in the lathe, a significant amount of torque is oftentimes necessary for revolving the spindle to effect the machining of a workpiece, and unlike the gear drive, the driving shaft that rotates with the driven small wheel cannot provide enough force to drive a loaded workpiece.